In a design stage of producing goods, design conditions are represented as a function (e.g. objective function, cost function or the like) of various parameters, and the parameters are optimized so that the value of the objective function becomes minimum, for example. In the design optimization of SRAM, while fluctuating values of several parameters to dozens of parameters, Simulation Program with Integrated Circuit Emphasis (SPICE) simulation is carried out for the corresponding shape to calculate a cost value with the cost function, and the shape minimizing the cost value is searched. However, when the number of parameters is large, there is a problem that it is impossible to obtain an optimum solution within a reasonable period of time, because the search space becomes broad and the number of times of the simulation increases.
Incidentally, a following technique for reducing the number of times of the simulation exists. Namely, in this technique, the influence of discrepancies of circuit element values due to the manufacturing process of the circuit or fluctuation of the use conditions to the circuit characteristics is analyzed. More specifically, after it is evaluated whether or not the distribution of the fluctuation factor parameters, which is determined by the Monte Carlo method, satisfies the analysis accuracy requested by the designer, the values of the fluctuation factor parameters are determined. Then, the minimum number of times of the circuit simulation, which satisfies the analysis accuracy requested by the designer is automatically determined. However, this technique does not use the characteristic peculiar to SRAM.
Namely, there is no conventional technique for reducing the number of times of the simulation to be carried out to generate a model expression for the SRAM design.